People rely on absorbent articles in their daily lives.
Absorbent articles, including adult incontinence articles, feminine care articles, and diapers, are generally manufactured by combining a substantially liquid-permeable topsheet; a substantially liquid-impermeable backsheet attached to the topsheet; and an absorbent core located between the topsheet and the backsheet. When the article is worn, the liquid-permeable topsheet is positioned next to the body of the wearer. The topsheet allows passage of bodily fluids into the absorbent core. The liquid-impermeable backsheet helps prevent leakage of fluids held in the absorbent core. The absorbent core is designed to have desirable physical properties, e.g. a high absorbent capacity and high absorption rate, so that bodily fluids may be transported from the skin of the wearer into the disposable absorbent article.
The present invention relates to water swellable, water insoluble superabsorbent materials, which are often employed in an absorbent core (also referred to as an absorbent composite), in part to help “lock up” fluids entering the core. More specifically, the present invention pertains to superabsorbent materials having a modified friction angle measured in a gel-bed of the superabsorbent material. The gel-bed friction angle of the superabsorbent materials of the present invention is controllable and follows a predetermined pattern. The present invention also relates to use of the controlled gel-bed friction angle superabsorbent materials in absorbent composites and absorbent articles incorporating such absorbent composites. Controlling the gel-bed friction angle of the superabsorbent materials may allow control of phenomena including, but not limited to: the swelling of the superabsorbent material, stresses experienced by the superabsorbent material and/or other ingredients (e.g., fibers) in an absorbent composite; the permeability of an absorbent composite containing the superabsorbent material; and/or, the absorbency, resiliency, and porosity of the absorbent composite. The present invention relates to treatments for superabsorbent materials to manipulate gel-bed friction angle and new superabsorbent materials having the desired gel-bed friction angle characteristics.
Absorbent composites used in absorbent articles typically consist of an absorbent material, such as a superabsorbent material, mixed with a composite matrix containing natural and/or synthetic fibers. As fluids enter the absorbent composite, the superabsorbent material swells as it absorbs the fluids. The superabsorbent material contacts the surrounding matrix components and possibly other superabsorbent material as it swells. The full swelling capacity of the superabsorbent material may be reduced due to stresses acting on the superabsorbent materials (e.g., stresses imposed by the matrix on superabsorbent material; external stresses acting on the absorbent composite that comprises a matrix and superabsorbent material, including, for example, stresses imposed on an absorbent composite by a wearer during use; stresses imposed by one portion of the superabsorbent material on another portion of the superabsorbent material, whether directly or indirectly; etc.). Furthermore, stresses acting on an absorbent composite comprising the superabsorbent material may act to reduce interstitial pore volume, i.e., space between superabsorbent material, fibers, other ingredients, or some combination thereof (without being bound to a particular analogy, and for purposes of explanation only, think of a force acting on some unit area of a sponge-like material with pores, with the force per unit area—i.e., stress—acting to reduce the thickness of the sponge-like material, and, therefore, the volume of the pores).
As the superabsorbent material swells, it may rearrange into void spaces of the absorbent composite matrix as well as expand readily against the matrix to create additional void space. Also, as the superabsorbent material swells, stresses acting within and/or on the absorbent composite may increase due—at least in part—to expansion of the superabsorbent material, thereby reducing the pore volume between: fibers, superabsorbent material, other ingredients in the absorbent composite, or some combination there of. The ability to rearrange within the composite matrix, and the magnitude and extent of the stresses acting within and on the composite matrix, depend on several factors specifically including a gel-bed friction angle of the superabsorbent material. In addition, as the superabsorbent material moves within the composite matrix, the superabsorbent material may contact the components, such as fibers and binding materials, of the surrounding matrix. Thus, the frictional properties of the superabsorbent material may influence the ability of the material to swell and rearrange or move within the matrix, as well as the magnitude and extent of the stresses acting within and on the composite matrix.
It is often desired that the superabsorbent material be able to rotate and translate within the voids of the absorbent composite to allow the superabsorbent material to swell as close to full swelling capacity as is possible within the matrix. There is a need for a superabsorbent material which may more easily rearrange within the void space of the absorbent composite matrix. There is a need for a way to control the physical mechanics that: allow the superabsorbent material to rearrange within the absorbent composite matrix; reduce or minimize the stresses acting within or on the absorbent composite or its ingredient(s); and/or reduce the reduction in pore volume that may accompany the build up of said stresses.